The design of a modern military fighter airplane involves the consideration of many important factors. When the design requirements for the fighter airplane include short field and/or vertical takeoff and landing capabilities, many of these factors assume an even greater importance.
For example, maneuverability is critical to a fighter airplane particularly with regard to the airplane's ability to turn quickly and tightly when engaged against an enemy airplane. Often, the airplane which is able to out-turn its opponent is able to successfully fire upon and destroy the opponent airplane. Conventional mechanisms have been used on fighter aircraft to change the wing configuration in order to allow the fighter to turn more rapidly or through a smaller radius.
During aerial combat maneuvering it is not uncommon for the airplane to be flown under high "g" conditions at angles of attack at or near stall. Often, this occurs during high "g" turns when attempting to maneuver into position to fire at an enemy airplane. During these high "g" turns, it is important that the airplane remain stable and under control of the pilot. An airplane which has stalled in an unbalanced condition will sometimes enter a spin. Failure to maintain control can result in the enemy airplane being able to gain an advantageous position to fire on and destroy the out-of-control airplane.
In addition to maximizing aircraft maneuverability, minimizing weight is another key design goal. An aircraft that is lighter generally can accelerate faster. In addition, when the aircraft has a short (or vertical) takeoff and landing requirement, weight reduction is critical to allowing the aircraft to achieve this goal.
Furthermore, systems that are simple generally have fewer parts and weigh less than more complicated systems. A further advantage of employing a mechanically simpler system is greater reliability as well as reduced maintenance. These factors are also important for a military airplane where access to proper maintenance is sometimes limited.
There are a number of conventional high lift devices for wings. For example, in U.S. Pat. No. 2,167,601 by Rose there is disclosed a movable leading edge device for a wing which in an extended position opens a passageway between the wing leading edge and the device to allow air flow from the bottom of the wing to the top of the wing.
In addition, U.S. Pat. No. 4,285,482 by Lewis, and assigned to the assignee of the present invention, pertains to a hinged leading edge high lift device which forms an aerodynamic slot in the extended position. On the other hand, U.S. Pat. No. 4,880,189 by Day pertains to a device for closing a slot which is present in the leading edge of a wing.
Other devices include those disclosed in U.S. Pat. No. 4,585,192 by Clifford-Jones which pertains to a mechanism for extending and retracting a leading edge slat; as well as U.S. Pat. No. 5,158,252 by Sakurai (assigned to the assignee of the present invention) which pertains to a leading edge flap having a variable camber surface; and U.S. Pat. No. 5,056,741 by Bliesner et al (also assigned to the assignee of the present invention) which pertains to a leading edge flap wherein the bluntness of the leading edge portion and the slot-gap width are varied.
Furthermore, U.S. Pat. No. 4,293,110 by Middleton et al (assigned to the assignee of the present invention) pertains to a leading edge flap for a supersonic airplane; and U.S. Pat. No. 3,375,998 by Alvarez-Calderon discloses a leading edge flap which combines the advantages of a Krueger type flap with those of a slotted leading edge flap.
And, French Patent No. 58,868 pertains to a slotted leading edge airfoil.